It is known that large diesel engines in particular are increasingly equipped with dual-flow air systems. Two turbochargers compress the two fresh air mass flows into one combined boost pressure. The exhaust gas mass flows drive the turbines of both turbochargers. An appropriate multi-channel air supply and an appropriate multi-channel exhaust gas discharge are provided in such a dual-flow or multi-flow air system. The exhaust gas is recirculated from the multi-channel exhaust gas discharge into the multi-channel air supply, and the exhaust gas recirculation is regulated for setting a setpoint fresh air mass flow.
Standard methods enable either a) the adjustment of the fresh air mass flow required for meeting the emission standard by activating the exhaust gas recirculation valves in the exhaust gas recirculation channels in an identical way or b) the adjustment of the individual air paths or air channels to the same overall proportion of the fresh air mass flow, in the case of a dual-flow air system to one half of the total fresh air mass flow. In theory, i.e., in the ideal case, involving balanced air paths or air channels and the same behavior of the exhaust gas recirculation valves, the emission standard is met and, simultaneously, an equal air mass flow is achieved in the existing air paths or air channels. In practice, all multi-flow air systems are asymmetrical and, as a rule, the exhaust gas recirculation valves exhibit different behaviors, e.g., due to manufacturing tolerances or aging. In case a), this results in unequal air mass flows in the individual air paths or air channels, which results in very low turbocharger rotational speeds. This in turn results in very poor startup behavior or in low agility. In contrast, in case b), the total setpoint (fresh) air mass flow is not achieved in border areas. In a dual-flow air system, a first controller for the exhaust gas recirculation of a first air channel or air path, for example, is operated within the limit of a manipulated variable in this case, and a second controller for the exhaust gas recirculation of a second air channel or air path regulates one half of the total setpoint (fresh) air mass flow required by it.